Of the different types of compressors, the reciprocating compressor is probably the most widely-used in transporting gas through pipelines and the like. In a reciprocating compressor, the gas is compressed by a piston which moves back and forth within a compression chamber formed within the "cylinder" of the compressor. These types of compressors usually have dual compression chambers within the cylinder whereupon a single piston becomes double-acting as it reciprocates in the cylinder. That is, the piston moves in a first direction to compressed gas in one compression chamber and expel it through an outlet or discharge valve while drawing gas into the other compression chamber through an inlet or suction valve. The operation is reversed when the piston moves in the opposite direction.
The overall efficiency of a reciprocating compressor is related to the "fixed clearance" of the compressor; "fixed clearance" being that volume remaining in the compression chamber when the reciprocating piston is at the end of its compression stroke. As will be recognized by those skilled in this art, for a compressor to reach its maximum efficiency for a particular set of operating conditions (e.g. horsepower available, composition of gas suction and discharge temperatures and pressures, etc.), it is necessary to adjust its fixed clearance to the smallest volume as is practical for such conditions. Since these conditions may vary from time to time during an on-going operation or from operation to operation, it is highly beneficial to be able to easily and quickly adjust the clearance of a compressor to optimize its efficiency for the then-existing conditions with only a minimum of downtime and expense.
There are at least two general types of reciprocating compressors; one where the suction and discharge valves are "in-line" within the cylinder and the other where the suction and discharge valves are radially mounted within the cylinder heads or within the cylinder wall. In one such in-line valve compressor, the suction valves, which may be adjusted to change the clearance, are positioned concentrically within the cylinder while the discharge valve is carried by the reciprocating piston, itself; see U.S. Pat. Nos. 5,011,383; 5,015,158; 5,141,413; and 5,209,647. In another known, in-line valve compressor, the suction valve is carried by the piston and the discharge valve is adjustably positioned within the cylinder whereby the clearance can be changed; see co-pending and commonly-assigned U.S. application Ser. No. 08/507,765, filed Jul. 26, 1995.
It has been found that by merely placing the valves in-line with the cylinder, it is possible to substantially reduce the fixed clearance for the compressor. Further, by making the position of one of the valves adjustable, this type of commercially-available compressor becomes very efficient in a large number of operations. However, since the mounting of a valve in a travelling piston limits how small the cylinder can be in in-line compressors of this type, there are still many every day operations in which in-line compressors can not be used economically. Accordingly, there are still a large number of gas-compressing operations where the more conventional, radial-valved compressors are much more economical to operate.
In known prior art, the "fixed clearance" of radial-valved compressors is adjusted by actually removing the suction and/or discharge valves from their respective radial bores and then adding or removing spacers before reassembling the valve(s) into its bore(s). The spacers adjust the operating position of a valve within its radial bore thereby either increasing or decreasing the "fixed clearance" of that particular compression chamber, as the case may be. As will be recognized, this technique is time consuming and can result in expensive downtime of the compressor. Further, since the spacers are of defined thicknesses, the amount of clearance can only be adjusted in set increments and accordingly, it is unlikely that the valve can be adjusted to an exact position which will produce the optimum efficiency for the compressor at the then-existing operating conditions.